As a basic industry of raw material, the steel industry has a strategic significance for the overall economy. As the competition increases in the market of steel, the demand for steel product is transformed from one single type of large batch to diversified types of small batches. However, this transformation may bring challenges to the steel plant. It is important to reduce the consumption of the resource and the production cost for slab production, while satisfying demands for diversified types of small batches.
As large equipment of high energy consumption, the steelmaking converter and the electric furnace have a high cost for startup and operation, and the capacity of the steelmaking line must be fully exploited for the steelmaking is a bottleneck process for overall capacity of the steel production. In order to gain a big share in the steel market, a steel plant must satisfy the diversified demands on the market, that lead to some differences of requirements in the intermediate order (the hot-rolled slab) or the final order (the hot-rolled strip steel) in terms of the steel grade, the specifications, the physical characteristics, the date of delivery, etc, and these differences will directly affect the charge plan for steelmaking, that is the batching of orders for each charge. As the market demand for steel tends to be diversified types of small batches, the total weight of slabs in the same charge plan is often lower than the minimum production amount required by steelmaking operation, which leaves over a lot of mis-order slabs. Besides, if the client's order is cancelled but the production for this order has started, mis-order slabs are also produced. Here, the mis-order slab means the slab which does not belong to any client's order. The generation of mis-order slabs significantly increases the inventory of slab yard. If these mis-order slabs are not fully utilized, it may also lead to resource waste caused by repeated steelmaking, the delayed delivery, large cut-loss and low hot charging rate, and hence, it not only increases the production cost and lowers customer's satisfaction, but also increases energy and resource consumption, increases the CO2 emissions, and increases the environment pollution. In order to overcome these drawbacks, the planners need to allocate the mis-order slabs to the orders that are unfulfilled by slabs, that is the mis-order slab matching plan.
Besides, sometimes the slabs and the orders need to be re-matched, i.e., the re-matching the slabs to orders, due to variation of the organization of the plant or the client's requirement, such as: (1) when the continuous caster is producing the slabs, due to adjustment of the width of the slabs, the specification of the transition slabs, which connect two slabs with different width, might not meet the requirement of the order, or the quality of the transition slabs, which connect two slabs with different steel grades, might not meet the requirement of the order due to casting of dissimilar steel grades (usually between steel grades close to each other), thus causing the undesired matching between the slabs and the orders; (2) some urgent orders (which have a urgent date of delivery) might lack slabs due to waste material of the post-process, and it is necessary to adjust the matching between the slabs and the orders to guarantee that the urgent orders can be delivered in time; (3) if the client's requirement for the steel grade, size and weight is varied, obviously the produced slabs according to original requirement cannot meet the changed requirement.
The slab matching plan includes mis-order slab matching plan and slab re-matching plan. Most steel plants have multiple hot rolling lines, the specification of slabs required by these lines might overlap in some extent. Due to the huge amount of data and complicatedness of the problems, planners usually consider the respective lines separately when making the mis-order slab matching plan and slab re-matching plan, but in the view of the overall process of hot rolling, such a scheme is not global optimal. Making mis-slab matching plan and slab re-matching plan for all the hot rolling lines simultaneously can effectively enlarge the optimal space, and hence reduce the production cost and the material consumption, improve the material resource utilization, and increase the profit and competitiveness of the plant.
Currently, in the steel plant, the mis-order slab matching and the slab re-matching plans are still made in a totally manual way. Most of the planners make the plans according to the table in an written form, and only a few of the planners do this job on an ERP information platform; but this ERP information platform still only provides information about data and cannot do the work of automatic optimization, and the planning is still based on personal experience and some simple rules. When facing the huge amount of information about data and the complicatedness of the matching rules, it is difficult for the planners to make an efficient scheme accurately and timely, which causes an undesired and un-optimal matching, thus resulting in low utilization of the slabs, high consumption of resource, high inventory level of slab yard, and delayed delivery of orders etc. Therefore, there is an urgent need for an optimization solution for the steel plant to solve the abovementioned problems efficiently and timely to reduce the production cost and inventory cost, reduce the resource and energy consumption, shorten the production cycle, and improve the capability of timely delivery.
Some patents and papers give their solutions on these problems. Tang et. al., (L. X. Tang, J. X. Luo, J. Y. Liu, Modelling and a Tabu Search Solution for the Slab Reallocation Problem in Steel Industry) and the U.S. Pat. No. 8,942,961 B2, titled “Re-matching method of slab-order for improving slab utilization in iron and steel plants” only discuss two types of method of slab re-matching for single production line, and gives solutions for different intelligent algorithms. In their problem, the mis-order slab matching scheme decision has already been given.
Vasko, et. al. (F. J. Vasko, M. L. Cregger, K. L. Stott, L. R>Woodyatt. Assigning slabs to orders: An example of appropriate model formulation. Computer & Industrial Engineering. 1994. 26: 797-800) and Tang Lixin, et. al., only discuss a matching method for slabs for single production line in the U.S. patent application Ser. No. 13/679,954, titled “Model and device for assigning surplus slabs in the slab yard before hot rolling process”. Therein, Vasko, et. al. study a slab matching method for slabs that can be cut with the objective of minimizing the cut loss of the slabs, while Tang Lixin, et. al., study a surplus slab matching method for slabs that cannot be cut aiming at multiple practical objectives including minimization of the cut loss of the slabs. They all did not give how to make re-matching plan for slabs and orders when the production variation occurs.
However, all these discussions are with respect to either the matching of left slabs or the re-matching of slabs for single production line, and do not consider the mis-order slab matching decision and slab re-matching decision simultaneously, do not involve the matching for multiple lines, and haven't take the position of the storage area, time in storage and the logistic expenses into consideration. Secondly, these discussions treat the slab matching and re-matching separately. The present invention considers the slab matching and the re-matching integrally to achieve the global optimization.